1. Field of the invention
The present invention is generally concerned with clutches with built-in travel limiting means. It is more particularly, but not exclusively, directed to multiple disk clutches and especially dual or twin disk clutches comprising two friction disks for fitting to industrial vehicles.
2. Description of the prior art
As is known, a clutch comprises, axially distributed along a common rotation axis, a reaction plate, an end friction disk, at least in the case of a multiple disk clutch, a pair of members comprising in succession an intermediate pressure plate and an intermediate friction disk, an end pressure plate and an annular cover attached to the reaction plate. The plates and the cover are constrained to rotate with a driving shaft whereas the disk is or the disks are constrained to rotate with at least one driven shaft.
In the case of a twin disk clutch the pressure plates are jointly acted on by engagement means which urge them continually towards the reaction plate; on the other hand, they are individually acted on by disengagement means urging them continually towards the cover.
During disengagement of a clutch of this kind it can happen that an intermediate disk remains gripped between the two pressure plates which are adjacent it. This results from the return action of the individual disengagement means which confer on each pressure plate a significant range of axial movement, variable from one plate to another.
At present there are various known devices intended to overcome this disadvantage. The guiding principle in the case of a twin disk clutch, for example, is to allow the intermediate pressure plate a predetermined range of axial movement, adjustable in the axial direction to take into account the reduction in the thickness of the friction disks resulting from wear thereof. Thus French Pat. No. 951 512 proposes a device in which an intermediate (or external) pressure plate has on its external periphery radial lugs, bored in the axial direction, intended to have pass through them guide pins attached to the reaction plate. The axial movement of a plate of this kind is controlled by intermediate members in the form of sleeves clamped onto the pins and at the ends of which there are flanges for limiting the axial displacement of the plate in question. The intermediate members are clamped onto the pins in such a way that they can slide on the pins when acted on by the engagement members but not when acted on by the disengagement means.
A device of this kind has the disadvantage that it leads to the onset of jamming or friction between the intermediate members and the bores in the lugs on the intermediate plate. The result is a reduction in the torque transmission capacity of the clutch, or the choice of otherwise unnecessarily large dimensions for the engagement means. Also, controlling the force with which the intermediate members are clamped to the shafts is a delicate process. Because of this, in order to produce a reliable clutch, it is necessary to use a non-negligible clamping force so as to be certain that the intermediate member will not move when acted on by the disengagement means. Furthermore, a device of this kind is of unpredictable behavior because of expansion and corrosion phenomena which may affect it. Finally, the fitting of a clutch equipped with this device is a delicate and complex matter by virtue of the presence of the pins.
French Pat. No. 2 118 761 describes a device in which a finger retained in position by a clamping bush tightly fitted into a housing on the cover passes through each peripheral lug on a pressure plate.
Abutment rings are fixed in position on said finger in the axial direction by means of a spacer and said bush. In addition to the disadvantage memtioned above in relation to the previous patent, this device involves high machining costs by virtue of the complex shapes of the finger and the housing in the cover.
Unlike the previous two patents, French Pat. No. 1 576 120 describes a twin disk clutch in which fingers which are unrestrained with regard to the reaction plate and the cover pass through the bores in the lugs on the intermediate pressure plate. These fingers comprise a split elastic bush gripped in a bore in a lug and in which are disposed plugs linked to one another by a radially expandable pin. Axial movement of the intermediate pressure plate is then controlled by abutment of said plugs on respective axial bearing surfaces formed on the cover and on the reaction plate. A device of this kind presents the same problems as previously with regard to controlling the clamping force between the finger and the bore in the lug of the pressure plate which results, as has already been mentioned, in the choice of otherwise unnecessarily large dimensions for the engagement means.
An objective of the present invention is to overcome the aforementioned disadvantages, and the invention is more particularly directed towards providing for optimum transmission of torque to the clutch. The invention is also intended to provide a multiple or single disk clutch of which the behavior in operation is as independent as possible of the environment, in particular expansion and/or corrosion phenomena.